Method of preparing acylated hydroxypolycarboxylic acid anhydrides



Patented Aug. 29, 1950 Marylou QF rRARING ACYLATED HY- foaoxrrorrcnanoxrrio non) anni@ 'Charles F. Fuchs, Chicago, Ill., assigner to The Emulsoi Corporation, lChica'goylll.; -a= corpora'- tion of Illinois f No Perline! 12 Claims.

My invention is directed to a new and useful method for 'the productionl'bf" certain-ac'ylfhydroxypolycarboxylio' 'i acid 1 anhydrides, i namely, those wherein the acylraldical '-isf'I at leastone member selected from' the'group c'nsis'tingof acetyl and propionyl radicals. 7 The preparation of Ysuch compounds, for eX- arnple, diacetyl'tartaric'acid anhydride, hasheretofo're been yknown? `This has' commonlybeen done by /admixing-tartarc acid 'with-an' excess 'of acetic `anhydrideY whereupon' fon cooling,v the' reacti'on product, comprising: mainly -"dia'cety1'-tar` taric'r acid "anhydride,v crystallizes -from-the mixture o acetic acido and excess "acetic anhydride and is collectedbyffiltratioii -f Such procedures have `a number' of objections.VV The mother liduor, resulting from the formation of the crystalline diacetyltartaric acidanhydrid reactionproduct, is'"strongly`acd 'and l achryrr'1`atoryad its'iha'ndling' and separation"arevv 'diflicult @In addition, due" to Athew solubility or the Yreaction product f in the mother liquor, a lower yield of the desired reaction' product res'ultsi" v Furthermore, since the mother liquorrv comprises a mixture of'various products', recovery of the diaoetylftartaricl-aoid anhydride 'therefrom isa diliicu-lt, c'o'stlyfan'd uneconoi'r'iic 'prcedure.`v Diac'tyl tartaric acid anhydride, when" preparedby'such known methods, is frequently' characterized byobjectionable lhygros'copicity and instability i In accordancewith my invention, the objections described above are overcome and the new and 'useful'method which' I describe in detail hereafte'rimakes possible the production of fac'yl hydroxypolycarboxylic acid 2 i aiihydrides'- in? la simple manner and 'one' adapted forlflarge'scale manufacturey thereof. The compounds "themselves are, moreover, readily recovered in excellent yields, in `a high degree of purity and are characterized by' substantial non-hygroscopicity ifa-nd stability.

'In general, my method comprises reacting an hydroxypolycarboxylicv acidwi'thv an anhydrideof atleast one acid'selected from the group'consisting of acetic acid vand propionic acid :in amount not substantially less than the' stoichiometric amount necessary to produce the acyl? hydroxypolycarboxylic acid anhydride; heating the "reaction mixture to distilloif the'exoess facid,.and recovering the acyl hydroxypolycarboxylic acid' anhydride." Itis particularly'advantageousv to u'tilizefrom about-3 vto about 5 mois, preferably about 3.1 to 3.5"mols, of'the acetic-'or-propionic facid anhydride foreach mol 'of di-hydroxy`di'-carboxylic acid; "as, vfor f example, i'tartaric' acid,="use`d infthe nmiiimifm November 10, 194s,

serial No. 59,411

reaction, and to carry out `the reaction in the presence v'ofl a catalyst, such as an acidic material, and' torecoverfthe-aforesaid acyl hydroxypolycarboxylic acid anhydride as a vmolten product. A suitable catalyst is sulfuric acid but it is preferable to use phosphoric acids, for example, concentrated (85%)' phosphoric acid since products oi lighter vcolorare obtained. Wherev a mono-hydroxy dior tri-carboxylic acid, as, for example-,ivc itricacid, is utilized, a minimum of 2 mois-off the acetic or propionic acid anhydride is employed and prererablyf from about 27.1 to l3.5 mois is utilized. `f In general, the minimum molal quantity offyacetic` or propio-nic acid anhydride utilized lfor each molyof hydroxypolycarboxylic acid is equal toor. not substantially less than the number oi hydroxy groups to be esteried plus an additional-mol for each-two carboxylic groupsto bring about anhydride formation. As a practical propositiom as lighl' excess over stoichiometric proportions is desirable. l n i y The hydroxypolycarboxylic acid is preferably used in a-dry vor substantially dry form. If it contains a small amount-of moisture, for example, of

theiorder o f labout-,1% .or'slightly more, the `utilization in the reaction mixture o f a proportionate excess amount of acetic or propionic acid anhydride willserve Atofeliminatesuchmoisture ,The 4following examplesare illustrative of particularlypreferred-embodiments of the practice otthevmethod. lt Wllbe understoodthat Vsaid examples-fare, accordingly, not to be construed in any Way= aslimitative of the full scope 10i the inventionsince various `changes may,be made, withinythe guidingv principlesv disclosed herein, with yrespect to reactants, temperatures, and times ofreactiongtheuse of.catalysts, if any,etc. :All parts mentionedareby-weight. A

.were 1 1375 parts of dry tartaric acid are placed in an acid-,resistant reaction "vessel, land' 29.50 y"partszof acetic anhydride 'and 0&5 :to: 0.8 part iof f concentrated Wad-'phosphoric acid are added.- 1 Anexothermic'"reaction1 starts soon; After.. the maximum` temperature has been reached, -whiclr f is usually4` 2:10a2305degrees the .reaction mixture is slowlyf heated` up to about :=240-.250 degrees??y While stirring. The-acetic' acid formed insthereaction is distilledofl; vpreferably by' graduallyiapplyingavacuum, which 'desirably should be: Iabout 26.-'to about -29';inches of: mercury'lattlie Aend/of the' vdistillation;-1 'About 2220'r partswoi practically pure glacial' A acetic' acid-"are therebyliRecovered. Byf-keeping thefreaction mixtur'eata suiiciently 3 high temperature, which is usually in the range of about 245-280 degrees F., practically all of the acetic acid is removed and the diacetyl tartaric acid anhydride remains as a molten product. The diacetyl tartaric acid anhydride product thus obtained may, if desired, be used in the same Vessel as an intermediate for the production of other compounds. If this is not to be done, the molten diacetyl tartaric acid anhydride may be drained from the reaction vessel and allowed to stand whereupon, on cooling, it solidies. The solid diacetyl tartaric acid anhydride is almost free of excess acetic acid and may be ground to a nely divided form if desired. The entire process can be iinished in 3 hours or less, depending upon the quantities prepared and the design of the plant equipment employed.

Example 2 1500 parts of dry tartaric acid, 4000 parts of propionic acid anhydride, and 0.5 to 1 part of concentrated phosphoric acid are reacted in the manner described in Example 1. The dipropionyl tartaric acid anhydride is recovered substantially free of propionic acid.

Example 3 1900 parts of dry citric acid, 2500 parts of acetic anhydride, and 0.5 to 1 part of concentrated sulfuric acid are reacted in the manner described in Example l. Acetyl citric acid anhydride is rccovered in a form substantially free from any acetic acid.

While the invention is particularly advantageous for the production of acetyl and propionyl tartaric and citric acid anhydrides, it will be understood that the principles may also be used for the production of acetyl and propionyl derivatives of other hydroxypolycarboxylic acid anhydrides such as those of malic acid, glutaric acid, and the like.

While the invention has been described in detail, the scope thereof is not to be limited except as is set forth in the appended claims.

What I claim as new and desire to protect by Letters Patent of the United States is:

l. A method of preparing acyl hydroxypolycarboxylic acid anhydrides in which the acyl radical is at least one member selected from the group consisting of acetyl and propionyl radicals, which comprises reacting an hydroxypolycarboxylic acid with an anhydride of at least one acid selected from the group consisting of acetic acid and propionic acid in amount not substantially less than 1 mol of said anhydride for each alcoholic hydroxy group present in said hydroxypolycarboxylic acid plus an additional mol of said anhydride for each two carboxyl groups present in said hydroxypolycarboxylic acid, heating the reaction mixture to distill off excess acid, and recovering the acyl hydroxypolycarboxylic acid anhydride.

2. A method of preparing acyl hydroxypolycarboxylic acid anhydrides in which the acyl radical is at least one member selected from the group consisting of acetyl and propionyl radicals, which comprises reacting an hydroxypolycarboxylic acid with an anhydride of at least one acid selected from the group consisting of acetic acid and propionic acid in amount not substantially less than 1 mol of said anhydride for each alcoholic hydroxy group present in said hydroxypolycarboxylic acid plus an additional mol of said anhydride for each two carboxyl groups present in said hydroxypolycarboxylic acid, said reaction being carried out in the presence of a small amount of an acidic catalyst, heating the reaction mixture to distill oi excess acid, and recovering the acyl hydroxypolycarboxylic acid anhydride.

3. A method of preparing acyl hydroxypolycarboxylic acid anhydrides in which the acyl radical is at least one member selected from the group consisting of acetyl and propionyl radicals, which comprises reacting an hydroxypolycarboxylic acid with an anhydride of at least one acid selected from the group consisting of acetic acid and propionic acid in amount not substantially less than 1 mol of said anhydride for each alcoholic hydroxy group present in said hydroxypolycarboxylic acid plus an additional mol of said -anhydride for each two carboxyl groups present in said hydroxypolycarboxylic acid, heating the reaction mixture in vacuo to distill off excess acid, and recovering the acyl hydroxypolycarboxylic acid anhydride. Y 4. A method of preparing acyl hydroxypolycarboxylic acid anhydrides in which the acyl radical is at least one member selected from the group consisting of acetyl and propionyl radicals, which comprises reacting an hydroxypolycarboxylic acid With an anhydride of at least one acid selected from the group consisting of acetic acid and propionic acid in amount in excess of 1 mol of said anhydride for each alcoholic hydroxy group present in said hydroxypolycarboxylic acid plus an additional mol of said anhydride for each two carboxyl groups present in said hydroxypolycarboxylic acid, said reaction being carried out in the presence of a small amount of an acidic catalyst, heating the reaction mixture in vacuo to distill off excess acid, and recovering the acyl hydroxypolycarboxylic ac.d anhyd. ide.

5. A method of preparing acyl hydroxypolycarboxylic acid anhydrides in which the acyl radical is at least one member selected from the group consisting of acetyl and propionyl radicals, which comprises reacting one mol of a dihydroxy dicarboxylic acid with from about 3 to about 5 mols of an anhydride of at least one acid selected from the group consisting of acetic acid and propionic acid, said reaction being carried out in the presence of a small amount of a phosphoric acid, gradually heating the reaction mixture, in vacuo, to distill 01T a major part of the excess organic acid, and recovering the acyl hydroxypolycarboxylic acid anhydride as a molten product.

6. A method of preparing acyl hydroxypolycarboxylic acid anhydrides in which the acyl radical is at least one member selected from the group consisting of acetyl and propionyl radicals, which comprises reacting an aliphatic hydroxypolycarboxylic acid having a total of up to 6 carbon atoms in its molecule with an anhydride of at least one acid selected from the group consisting of acetic acid and propionic acid in amount not substantially less than 1 mol of said anhydride for each alcoholic hydroxy group present in said hydroxypolycarboxylic acid plus an additional mol of said anhydride for each two carboxyl groups present in said hydroxypolycarboxylic acid, heating the reaction mixture, in vacuo, to distill oil a major part of the excess acid, and recovering the acyl hydroxypolycarboxylic acid anhydride as a molten product.

7. A method of preparing diacetyl tartaric acid anhydride which comprises reacting tartaric acid with acetic acid anhydride in a molal ratio of 1 mol of tartaric acid to not substantially less than 3 mols of acetic acid anhydride, heating the reaction mixture to distill off excess acetic acid, and recovering the diacetyl tartaric acid anhydride.

8. A method of preparing diacetyl tartaric acid anhydride which comprises reacting tartaric acid with acetic acid anhydride in a molal ratio of 1 mol of tartaric acid to not substantially less than 3 mols of acetic acid anhydride, gradually heating the reaction mixture, in vacuo, to a temperature in the range of about 230 to about 280 degrees F. to distill off a major part of the excess acetic acid, and recovering the diacetyl tartaric acid anhydride as a molten product.

9. A method of preparing diacetyl tartaric acid anhydride which comprises reacting one mol of tartaric acid with from about 3 to about 5 mols of acetic acid anhydride, said reaction being carried out in the presence of a small amount of phosphoric acid, gradually heating the reaction mixture, in vacuo, to a temperature in the range of about 230 to about 280 degrees F. to distill off excess acetic acid, and recovering the diacetyl tartaric acid anhydride as a molten product.

10. A method of preparing acetyl citric acid anhydride which comprises reacting citric acid With acetic acid anhydride in a molal ratio of 1 mol of citric acid to not substantially less than 2 mols of acetic acid anhydride, heating the reaction mixture, in vacuo, to distill off excess acetic acid, and recovering the acetyl citric acid anhydride as a molten product.

11. A method of preparing diacetyl tartaric acid anhydride which comprises reacting 1 mol of tartaric acid with from about 3.1 to 3.5 mols of acetic acid anhydride, gradually heating the reaction mixture, in vacuo, to a temperature in the range of about 230 to about 280 degrees F. to distill ori excess acetic acid, and recovering the diacetyl tartaric acid anhydride as a molten product.

12. A method of preparing diacetyl tartaric acid anhydride which comprises reacting 1 m01 of tartaric acid with from about 3.1 to 3.5 mols of acetic acid anhydride, said reaction being carried out in the presence of a small amount of phosphoric acid, gradually heating the reaction mixture, in vacuo, to a temperature in the range of about 230 to about 280 degrees F. to distill o excess acetic acid, and recovering the diacetyl tartaric acid anhydride as a molten product.

CHARLES F. EUCHS.

REFEREN S CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,872,029 Dreyfus Aug. 16, 1932 2,258,947 Crowell Oct. 14, 1941 OTHER REFERENCES Lucas et al., American Chemical Society Journal, v. 63, June 1941, page 1655. 

12. A METHOD OF PREPARING DIACETYL TARTARIC ACID ANHYDRIDE WHICH COMPRISES REACTING 1 MOL OF TARTARIC ACID WITH FROM ABOUT 3.1 TO 3.5 MOLS OF ACETIC ACID ANHYDRIDE, SAID REACTION BEING CARRIED OUT IN THE PRESENCE OF A SMALL AMOUNT OF PHOSPHORIC ACID, GRADUALLY HEATING THE REACTION MIXTURE, IN VACUO, TO A TEMPERATURE IN THE RANGE OF ABOUT 230 TO ABOUT 280 DEGREES F. TO DISTILL OFF EXCESS ACETIC ACID, AND RECOVERING THE DIACETYL TARTARIC ACID ANHYDRIDE AS A MOLTEN PRODUCT. 